This application relates to circuit packages for integrated circuits and, more particularly, to circuit packages that include metal flanges and high-temperature thermoplastic frames.
Semiconductor and other integrated circuit devices (sometimes referred to as “chips” or “die”) are typically mounted inside circuit packages to protect the die and to facilitate electrically, mechanically and thermally connecting the die to printed circuit boards, heat sinks and the like. A typical circuit package includes a base (commonly referred to as a “slug” or “flange”), a protective insulating housing and leads extending through the housing. Inside the housing, the leads are electrically bonded directly, or more commonly by wires, to contacts on the die.
The protective housing is made of a dielectric material, such as plastic or ceramic, and is attached to the flange to encapsulate the die and bonding wires and to protect them against intrusion of water vapor and other atmospheric gases. Most protective housings comprise two pieces, i.e. a set of sidewalls (a “frame”) and a lid, although some housings are molded as one-piece assemblies. The order in which the frame and the die are attached to the flange varies, depending on the material of the frame and, more particularly, the maximum temperature the material can tolerate without deforming or being otherwise damaged.
A circuit package for a high-power die typically includes a metal flange, to which the die is attached, often by eutectic soldering. The flange typically provides mounting features, such as screw holes or slots, by which the circuit package can be mounted, such as to a heat sink. In use, the flange conducts heat from the die to the heat sink.
The high temperature used to attach a die to a flange can damage or deform plastic, however ceramic materials are able to withstand this high temperature. A circuit package that employs a ceramic frame can, therefore, be assembled prior to the attachment of the die. A lid is then adhered to the frame, such as by epoxy.
To match the coefficients of thermal expansion of ceramic frames, flanges for these frames are typically made of a copper-tungsten alloy by a powder metallurgy infiltration process. This process is very expensive, and the thermal conductivity of the resulting alloy is limited. Improved thermal conductivity can be achieved through the use of copper-molybdenum-copper laminated flanges fabricated by an infiltration process followed by a lamination process, however these processes are very expensive.
Alternatively, the die can be attached to the flange prior to attaching the frame and lid. This approach enables use of low-temperature plastic for the frame, however adhesives used to attach the frame to the flange and to the lid perform less than satisfactorily. These adhesives often create imperfect seals or permit gaps to open during use of the circuit package. Furthermore, users of circuit packages prefer not to inventory flanges, frames and lids and assemble these pieces after attaching die to flanges.